A variety of alternative in vitro antitumor assays are being developed and comparatively evaluated with a view toward possible applications in primary (Stage I) screening or to help prioritize (Stage II) new agents for further study. Specifically, new methods are being explored for determination of cell survivorship of drug treatment; recovery of proliferative capacity following drug treatment; kinetics of drug action; pulse duration effects on cellular responses; and optimization of in vitro chemotherapeutic schedules. Moreover, methods for assessment of the above not only in monolayer culture but also in single-cell suspensions, weakly adherent lines, floating aggregates and spheroids are being pursued.